1. Field of the Invention
The invention relates to a failure diagnostic apparatus and a method of storing information failure. More particularly, the invention relates to a failure diagnostic apparatus and a method of storing failure information that easily determine the environment in which the condition of a vehicle is examined.
2. Description of the Related Art
Recently, it has been made mandatory to provide an On-Board Diagnostic-II (hereinafter, referred to as “OBD-II”) system in vehicles such as automobiles, to prevent air pollution. The OBD-II system provides a warning to a driver if a failure occurs in an exhaust gas control device. In the OBD-II system, information regarding a failure is stored in non-volatile memory of an Electronic Control Unit (hereinafter, referred to as “ECU”).
More specifically, in the OBD-II system, a Diagnostic Trouble Code (hereinafter, referred to as “DTC”), which contains information about a failure, is stored in the non-volatile memory. The DTC stored in the non-volatile memory is later retrieved using a scan tool so that the cause of the failure can be determined. The scan tool is a device dedicated to retrieving the DTC. After the cause of the failure is determined, and the cause of the failure is corrected by appropriate repair, the DTC stored in the non-volatile memory is erased using the erase function of the scan tool.
Japanese Utility Model Application Publication No. 2-49772 describes an airbag system that includes volatile memory and non-volatile memory provided in an ECU. The volatile memory or the non-volatile memory is appropriately selected to store the information about a failure that occurs in, for example, a collision detection portion in the airbag system. The response speed of the volatile memory is high, and the volatile memory is suitable for temporarily retaining records. Therefore, information that is frequently updated is stored in the volatile memory. For example, if a failure time is updated every one second or every one minute, the information on the failure time is stored in the volatile memory. In contrast, the non-volatile memory is suitable for permanently retaining records. Therefore, the information that is not updated frequently is stored in the non-volatile memory. For example, if the failure time is updated once every hour, the failure time is stored in the non-volatile memory.
Emission regulations tend to be tightened to take further measures against air pollution. Therefore, further requirements for the OBD-II system will be set. Particularly, it will be required to prohibit the DTC stored in the non-volatile memory from being erased by the scan tool, to more reliably retain the DTC.
In the system described in the above-described publication, the DTC about a failure is stored in the non-volatile memory. Therefore, even if a failure occurs, for example, in an assembly process when a vehicle is manufactured at a factory, the DTC about the failure is stored in the non-volatile memory in the same way as the DTC about the failure that occurred when a driver used the vehicle. Accordingly, if the DTC is prohibited from being erased in the OBD-II, the DTC about the failure that occurred when the vehicle was manufactured at the factory cannot be erased. In this case, when the DTC is retrieved using the scan tool, it cannot be determined whether the DTC was stored due to a failure that occurred when the vehicle was manufactured at the factory, or due to a failure that occurred when a driver used the vehicle.